SUBTHRESHOLD OSCILLATIONS AND RESONANT BEHAVIOR - 2 MANIFESTATIONS OFTHE SAME MECHANISM

The ability to generate subthreshold membrane potential oscillations i n neurons from the inferior olive nucleus has been attributed to the e lectrical properties of these neurons, as well as to the properties of the network. In the present in vitro study we quantitatively characte rized both intrinsic membrane and network properties that are directly involved in the oscillatory activity of olivary neurons in the guinea -pig. We also implemented an alternating current analysis to explore t he resonance behavior of these neurons and to compare the resonant pro perties with the properties of the oscillatory activity. Spectral anal ysis, used for the quantitative characterization of the oscillatory ac tivity under various experimental conditions, revealed that the patter n of the oscillatory activity is network specific rather than cell spe cific. These results are in agreement with the hypothesis that the osc illatory activity of olivary neurons is generated by a network of elec trically coupled neurons. Using alternating current analysis; we found that impedance-frequency curves of olivary neurons demonstrate a peak impedance (resonance) al a frequency between 3 and 10 Hz, which corre sponds to the frequency of the spontaneous oscillations. Like the spon taneous oscillations, this peak is tetrodotoxin insensitive, unaffecte d by K+ channel blockers and almost completely blocked in the presence of Ni2+ in the physiological solution. Increasing the temperature inc reases the resonance frequency. as well as the frequency of the sponta neous oscillations. These results show that the resonant behavior of i ndividual neurons is the basis of the oscillatory behavior of the netw ork and that resonance can serve as a lumped parameter which encodes t he oscillatory tendency of a neuron. (C) 1997 IBRO. Published by Elsev ier Science Ltd.